How can roadway ice form?
To get ice on a roadway requires freezing temperatures (below 32F) and moisture (water) at the surface, a combination that can occur in a number of ways: • Frost • Fog passing over a cold roadway surface • Freezing of groundwater seepage or melted snow • Freezing of snow that had initially melted on a warm road surface. • Freezing rain. More than one of these icing mechanisms can occur at the same time! Let us consider these icing processes one at a time. Frost Frost tends to occur on cold, relatively clear nights when wind speeds are low (less than 10 mph in general). But why are clear skies and light winds important? All objects give off or emit infrared radiation. The warmer the object the more infrared radiation it emits. We all have some experience with infrared radiation; for example, when you sit across a room from a fire you can feel the infrared radiation it emits. Some objects emit infrared radiation better than others. For example, the earth’s surface is far more efficient i
